1. Field of the Invention
The present invention relates to an image forming apparatus and a method of driving a liquid ejecting head.
2. Description of the Related Art
Inkjet recording apparatuses or similar apparatuses, which are image forming apparatuses of a liquid ejection recording system with a recording head of a liquid ejecting head (droplet ejecting head) that ejects droplets, have been known as image forming apparatuses such as printers, facsimiles, copying machines, plotters, and multifunction peripherals of these.
Japanese Patent Application Laid-open No. 2005-231174 discloses a method of controlling driving of a liquid ejecting head used in an image forming apparatus. In the method, after a driving pulse (droplet ejecting pulse) for ejecting a droplet is applied, a vibration suppressing pulse (non-ejecting pulse) with a pulse width Pws is applied (0.9 to 1.1)×((5/4)Tc−(Pws/2)) after the rising edge of the droplet ejecting pulse, where Tc denotes a natural vibration period in an individual liquid chamber (individual passage), in order to suppress the vibration due to droplet ejection.
As described above, as the timing of applying a residual vibration suppressing pulse, the time from the end of an ejecting pulse for ejecting a droplet to the midpoint of a pulse width Pw of the residual vibration suppressing pulse has been set to (5/4)Tc, thereby enabling the residual vibration to be suppressed most effectively.
However, when multi-pulse driving is performed for, for example, forming a single dot by merging a plurality of ejected droplets in flight, the residual vibration of the meniscus after the droplet ejection is formed by superposition of vibrations caused by a plurality of ejecting pulses. The phase of the residual vibration in this case is different from that of the residual vibration when a droplet is ejected with a single pulse.
In particular, the attenuation of the residual vibration of the meniscus is slow at a low viscosity, and thus the previous residual vibration remains strong at the time of the subsequent droplet ejection, resulting in a large phase difference.
This means that the conventional timing mentioned above for applying the residual vibration suppressing pulse deviates from an optimal timing due to the phase difference. The residual vibration suppressing pulse thus more greatly deviates from the optimal timing at a lower viscosity at which the attenuation speed of the residual vibration decreases and suppression is more required.
Sufficient vibration suppression effect thus cannot be obtained, causing defects such as a curved droplet and liquid overflow during the subsequent droplet ejection.
In view of the above, there is a need to enables residual vibration to be suppressed effectively even when a single dot is formed by ejecting a plurality of droplets.